1. Field of the Invention
The invention relates to devices for selectively deactivating cylinders of internal combustion engines to improve operating economy under low-load operating conditions.
2. Description of the Prior Art
A number of systems for selectively deactivating cylinders of internal combustion engines have been proposed. One such system is disclosed in U.S. Pat. No. 4,168,449, wherein a hydraulically actuated device attached to a stud extending from the head of the engine engages a rocker ball about which the rocker arm pivots during normal engine operation. The normal fulcrum point for the rocker arm is maintained when the hydraulic device is actuated. The hydraulic device includes a piston which forces three rods against the sleeve, the lower end of which engages the rocker ball. When the hydraulic pressure is released, the rocker ball is no longer maintained in fixed relationship to the stud, so that when the push rod forces one end of the rocker arm upward, the rocker ball yields to the rocker arm and does not act as a fulcrum therefore. This prevents the corresponding valve from opening. The device disclosed in U.S. Pat. No. 4,169,449 has numerous shortcomings, one of the most serious of which is that when the engine is operating, there is little or no downward pressure continuously exerted on the push rods for "deactivated" cylinders, while there is a very large downward pressure exerted on by the push rod end of the rocker arms for "activated" or normally operating cylinders (due to the forces exerted on the opposite ends of the rocker arms by the valve springs of open valves.) This imbalance results in "lash" or shock in the timing gears and timing belts that drive the camshaft of the engine. Such shock causes excessively loud engine operating noise, especially in engines which are somewhat worn (due to use). Further, the imbalance and resulting lash or shock substantially decreases the normal life expectancy of timing gears and timing belts causing unexpected failures.
Accordingly, it is an object of the invention to provide a cylinder deactivation system which does not produce substantially increased noise in an operating engine.
It is another object of the invention to provide a cylinder deactivation system which does not result in excessive wear of timing gears or timing belt components in an internal combustion engine.
The above mentioned three rods which engage the hydraulic piston and the above mentioned cylinder deactivation system experience an undue amount of wear. Furthermore, fitting of the system described in U.S. Pat. No. 4,169,449 usually requires "tapping into" the hydraulic system which operates the power steering unit of an automobile, increasing the likelihood of a leak in that system and loss of power steering due to leakage or other malfunction. If the above described cylinder deactivation device is to be retrofitted to an automobile which does not have power steering, a hydraulic fluid pump must be installed, greatly increasing the expense of providing the deactivation system on that automobile.
Furthermore, the deactivation system disclosed in U.S. Pat. No. 4,169,449 causes the deactivable cylinders to be deactivated when the engine is not running because the hydraulic pressure does not exist when the engine is off. This means that only the non-deactivable cylinders can fire during starting of the engine, so an engine using the system of U.S. Pat. No. 4,169,449 experiences difficult starting. Furthermore, if the engine has a tendency to "diesel" when the engine is turned off, this tendency becomes more pronounced, due to the loss of hydraulic pressure that deactivates some of the cylinders thereby reducing the amount of "load" on the dieseling cylinders.
Accordingly, it is another object of the invention to provide a cylinder deactivation system which does not require a hydraulic fluid pump.
The cylinder deactivation system disclosed in U.S. Pat. No. 4,169,449 is unduly complex in that it requires a large number of high precision, expensive components. The complex design results in unduly low reliability and high cost.
Therefore, it is another object of the invention to provide a cylinder deactivation system that requires relatively few components and is inexpensive to manufacture and install in an automobile engine.
A number of other cylinder deactivation systems, including those disclosed in U.S. Pat. Nos. 4,204,512, 4,096,845, 4,141,333, 4,114,588, 4,187,824, and 4,161,938 all have various serious disadvantages which make them unduly expensive, unreliable, and unsuitable for being retrofitted to most previously manufactured automobile engines.
Another cylinder deactivation system, which is available on 1981 Cadillac automobiles, includes an assembly having a solenoid and two movable fulcrum members which rest against rocker pivots. The device is attached to the cylinder head by means of two bolts which respectively pass through the two respective movable fulcrum members, rocker pivots and rocker arms. Compression springs inside each of the movable fulcrum members engage a plate from which four pegs extend upwardly. A slotted disc is rotatably disposed at the upper end of each of the two cylindrical fulcrum members. If the disc is aligned with the pegs, the pegs pass through the slots of the disc, allowing the fulcrum member and rocker pivot to yield to the rocker arm from opening a valve. However, if the pegs and the slots in the disc are not aligned, the movable fulcrum member maintains the rocker pivot in a fixed position, so that when the push rod is raised, the rocker arm pivots about the rocker pivots, causing a valve of the engine to open. The foregoing is not suitable for adaptation to other types of previously manufactured engines because it is completely unadjustable, so that it can not be installed on engine having normal studs. Furthermore, when the subject cylinder is activated, the pegs "hammer" against the rotating discs each time the corresponding push rod is raised. It would appear that this hammering would result in undue engine wear and engine noise.
It is therefore another object of the invention to provide an improved, low cost, highly reliable cylinder deactivation system which avoids the shortcomings of the prior art.
Another object of the invention is to provide a low cost, reliable cylinder deactivation system which is easily installed on prior external combustion engines.